A Soil Test

A basic soil test can tell a lot about your soil’s ability to sustain healthy plant growth. Furthermore a soil test is an easy test to complete and professional interpretation is rarely more than $20. What to stops most people doing a soil test is a lack of time and a lack of knowledge.

What the soil test will tell you

pH of the soil: most plants like a pH of around 6.5 – 6.8. This is slightly in the acidic range. Some plants such as lavender, and some lawns, prefer a slightly sweeter soil that is nearer 7.0, and others such as azaleas and rhododendrons like a more acidic soil closer to 5.5 or 6.0. So clearly it helps to know what you want to grow in the area of the soil test. However a general soil test will give you a starting point.

Nutrients in the Soil: Nitrogen, Potassium and Phosphorus are the basic three nutrients that all plants need. The soil test will tell you how much of each you have and if you need to add a specific nutrient to the garden. Micronutrients such as boron, magnesium and calcium will also be assessed.

Cation Exchange Capacity (C.E.C): Plants need to be able to access the nutrients in the soil. The nutrients that are absorbed is based on how many positively charged ions (such as Mg+, Ca+) can attach themselves to negatively charged particles in the soil. Clay and organic matter are the prime contributors of negative ions. If the positive ions cannot attach to anything they flow out of the soil. Thus the exchange capacity is an indicator of how well your soil will grab the nutrients and give them to the plant root. Low cation exchange indicates that the nutrients cannot attach and stay in the soil, before being leached away with moisture. Sands typically have low cation exchange numbers.

From these numbers the testing authority will advise you as to the health of your soil. They will usually give information as to how much lime, or other amendment, needs to be added to optimize your soil’s potential.

How to do a Soil Test

Soil tests are simple. You get a bucket or large garbage bag and go into the garden with a spade. Dig a small hole to a depth of four to six inches, and take a cup of soil from the base of the hole. Refill the hole. If you are doing the vegetable plot and need just a result for that area, then transfer the soil directly to a plastic bag. If you want a general result for the garden as a whole, then take several samples from different areas, and mix them together, before putting one cup into the bag. Most County Extension Services will provide you with information about where to send the sample. A few states will do in-house soil tests, others use private laboratories. The testing fee is generally under $20 regardless of where it is done. The results are usually available with 10 – 14 days. If you need help interpreting the results, contact your Extension Educator who will be glad to assist you.

With a soil test and a soil profile, you will be all set for a successful growing season.